In recent years, the systems of recording images by use of silver halide grains as sensitive elements and reproducing the images by so-called development processing to store them have been remarkably developed, and have been applied to various fields. Indeed, the market of color photography, which many people utilize for recording and enjoyment, has been continuously enlarged year after year. In particular, for the production of color prints, a demand towards finishing in a short period of time has increased, and high efficiency and high productivity have been increasingly required.
A color print finishing stage comprises, as well-known, exposure of photographic materials for prints which is performed by recording images on negative films and color development processing of the exposed photographic materials. The use of highly sensitive photographic materials results in a reduction in exposure time. On the other hand, in order to shorten the time of color development, it is necessary to use photographic materials capable of speeding development.
As techniques for solving such problems, the methods of processing color photographic materials containing so-called high silver chloride emulsions increased in silver chloride content, instead of silver chlorobromide emulsions which are high in silver bromide content, which have been widely used for photographic materials for color prints (hereinafter referred to as color photographic paper) are known. For example, PCT International Publication No. WO87/04534 discloses the method of processing rapidly, color photographic paper comprising a high silver chloride emulsion with a color developing solution substantially free of sulfite ions and benzyl alcohol.
For the purpose of providing a system capable of processing color photographic paper rapidly, attempts to put silver halide emulsions high in silver chloride content to practical use have been intensively made. It is known that silver halide emulsions high in silver chloride content are liable to produce fog and high sensitivity is difficult to attain. It is also known that such silver halide emulsions are apt to cause so-called reciprocity law failure, in which the sensitivity and the gradation fluctuate with a change in exposure illuminance. Further, it is known that the sensitivity is liable to fluctuate with a change in temperature upon exposure. These disadvantages have seriously hindered the high silver chloride emulsions from being commonly used in photographic practice.
In order to solve the above-described disadvantages of the high silver chloride emulsions, many techniques have been reported.
For example, JP-A-58-95736 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-58-108533, JP-A-60-22284 and JP-A-60-222845 disclose high content silver chloride emulsions having various grain structures containing layers high in silver bromide content in the silver halide grains to give high sensitivity, while repressing the fog of the high silver chloride emulsions. As a result of studies conducted by the present inventors, high sensitive emulsion materials could be obtained according to these techniques. However, it was discovered that desensitizing easily took place when pressure was applied to the emulsion grains, which resulted in a defect.
On the other hand, JP-A-51-139323, JP-A-59-171947 and British Patent 2,109,576A disclose that the addition of group VIII metal compounds results in high sensitivity and in an improvement in reciprocity law failure. Further, JP-B-49-33781 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-50-23618, JP-A-52-18310, JP-A-58-15952, JP-A-59-214028, JP-A-61-67845, West German Patents 2,226,877 and 2,708,466, and U.S. Pat. No. 3,703,584 disclose the addition of rhodium compounds or iridium compounds to achieve a high contrast and an improvement in reciprocity law failure. When the rhodium compounds are used, however, although hard emulsions can be obtained, significant desensitizing takes place. This is practically unfavorable. When the iridium compounds are used, the so-called latent image sensitization, i.e., the increase in development density with an elapse of time from the exposure of the photographic materials to the processing, is often observed. This is also unfavorable.
Furthermore, U.S. Pat. No. 4,269,927 discloses that high sensitivity can be obtained by adding cadmium, lead, copper, zinc or a mixture thereof to the inside of surface latent image type high silver chloride emulsion grains. Although this method gives the effect of slightly increasing the sensitivity and improving the reciprocity law failure, a fluctuation in sensitivity with a change in temperature upon exposure is not a sufficient improvement.
In addition, JP-B-48-35373 discloses that hard black and white photographic paper can be obtained at low cost by adding water-soluble iron compounds to silver chloride emulsions obtained by normal precipitation methods. Although the sensitivity of the silver chloride emulsions at high illuminance is surely increased by this method, a fluctuation in sensitivity with a change in temperature, particularly the temperature dependency of the sensitivity at high exposure illuminance, is not a sufficient improvement.
Further, JP-A-l-183647 discloses forming silver bromide-localized layers in the inside or on the surface of high silver chloride emulsion grains containing iron ions, whereby high sensitivity is obtained and further the fluctuation in sensitivity with a change in temperature upon exposure can be reduced. However, according to this method, the temperature dependency of the sensitivity at high exposure illuminance, is not improved sufficiently.